In the formation of integrated circuits, the gates of transistors are formed using either the gate-first approach or the gate-last approach. In the gate-first approach, polysilicon is often used to form the gate electrodes of the transistors. The formation of the polysilicon gate electrodes includes depositing a blanket polysilicon layer, and then etching the blanket polysilicon layer. The remaining portions of the polysilicon layer are the gate electrodes.
In the gate-last approach, metals are often used to form the gate electrodes of the transistors. The formation of the metal gates may include forming dummy gate electrodes, and then removing the dummy gate electrodes to form recesses. A suitable metallic material is then filled into the recesses, followed by a Chemical Mechanical Polish (CMP) to remove the excess portions of the metallic material. The remaining portions of the metallic material left in the recesses form replacement gates for the respective transistors.